It is well known to provide an air bag assembly including an inflatable air bag cushion for protecting the occupants of a transportation vehicle. In an automotive vehicle such air bag assemblies are typically located within the hub of the steering wheel and in a recess in the instrument panel for protection of the vehicle occupants seated in opposing relation to such assemblies. Additional air bag assemblies may be located within the seats and/or door panels for protection of the occupants during a side-impact event.
Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing certain predetermined vehicle conditions, such as a certain level of vehicle deceleration, the inflator discharges a fixed amount of inflator gas thereby forcing the air bag into a deployed position. The inflator gas occupies the available volume within the air bag cushion thereby forcing the air bag cushion to expand outwardly to the extent permitted by its construction. As the occupant comes into contact with the expanded air bag, the inflator gas is forced out of the air bag thereby dissipating the kinetic energy of the occupant.
Absent restraint, an inflated body tends to assume a generally spherical profile. In order to provide control over the inflated shape of the air bag cushion, it is known to utilize tethering elements in the form of straps or webs extending between surfaces of the air bag cushion to thereby hold the surfaces in fixed orientation relative to one another upon inflation. The selection and length of such tethering elements can thus be used to establish a desired inflated profile. However, once the tethering elements are attached in fixed relation to the surface of the air bag cushion, the inflated geometry of the cushion is likewise fixed and is not subject to adjustment.
It has been recognized that the preferred inflated profile of the air bag cushion may vary depending upon the severity of the activating impact event and/or upon the size and position of the occupant to be protected. Thus, the ability to effectively control the inflation characteristics of the air bag cushion is potentially desirable. In order to provide a degree of control over the inflated profile of the air bag cushion it is known to use an inflator that has varied levels or stages of inflator gas output in response to the sensing of different vehicle occupant conditions. Thus, it is generally known in the prior art to utilize so-called “dual-stage” inflators that discharge predetermined amounts of gas at one or two levels. However, the use of such “dual-stage” inflators provides control over only the amount of inflator gas which is discharged and does not provide control over the expanded geometry of the inflated air bag cushion. That is, due to the compressible nature of the inflation gas, so long as the air bag has a fixed volumetric capacity, the inflator gas will tend to fill that capacity and the expanded configuration of the air bag will be generally the same although the pressure may vary.
In order to provide an additional level of control over the air bag performance it has been suggested to utilize air bag cushions which incorporate sewn or woven in seams within the air bag to control the expanded geometry of the inflated air bag. Such seams separate upon the introduction of pressures exceeding a certain level thereby freeing the air bag cushion from the restraint imposed by the seams at lower pressures. In order for such break-away seams to provide controlled expansion, the introduction of such seams must be carried out with substantial precision such that seam separation will occur in a highly reproducible and predictable manner. In some instances, such requisite precision and reproducibility may be difficult to achieve. Moreover, even when such break-away seams are utilized, the expansion which occurs may be in all directions. In some applications it is believed that preferential expansion in the depth of the air bag (i.e. towards the occupant to be protected) may be desirable.
In order to address the desire to provide enhanced control over the final inflated profile of the air bag, it has been proposed to utilize release mechanisms to hold tether straps in place under normal conditions and to release the straps in situations where an extended profile is desired. By way of example only, and not limitation, various release mechanisms are illustrated and described in U.S. Pat. No. 6,390,501 to Greib et al., U.S. Pat. No. 6,422,597 to Pinsenschaum et al. and U.S. Pat. No. 6,454,300 to Dunkle et al., the contents of all of which are incorporated by reference as if fully set forth herein.